DMeyer and Flyboy are correct.

The JR is a standard type cable, used in other electronic applications. No problem using an off-the-shelf cable. Or, if you have the skill to make cables, by all means go ahead. Hitec, Futaba & Airtronics are a different story, and yes, the Hitec cable has a specific end for the instructor's transmitter.

And yes, 5 or 6 feet of cable is sufficient. With more cable, you can step on it pretty easy.

Best wishes for success in your training!
Dave Olson